1. Technical Field of the Invention
This invention relates generally to in-band on-channel broadcasting and more particularly to in-band on-channel broadcasting using a mesh network.
2. Description of Related Art
In the United States each analog FM radio station is assigned a channel centered on a particular frequency, with spacing of 0.2 MHz between channels. If an analog radio station is, for example, assigned a frequency of 93.7 MHz, the next station cannot be closer than 93.5 MHz or 93.9 MHz. An analog FM station, however, does not actually need to use the entire 0.2 MHz bandwidth for broadcasting the FM signal. Even leaving room for a guard band to help protect against interference from adjacent stations, there is enough remaining bandwidth to accommodate the transmission of digital signals within the 0.2 MHz of bandwidth allocated to the FM radio station.
Broadcasting both digital and analog radio signals in the same portion of the radio frequency spectrum previously used to broadcast only the analog radio station, 0.2 MHz in this example, is referred to generically as in-band on-channel (IBOC) broadcasting. Many members of the public know in-band on-channel broadcasting by the name HD Radio, which is a brand name used by iBiquity®.
As illustrated in prior art FIG. 1, current systems perform IBOC broadcasting by transmitting both the digital and analog radio signals from one location using separate antenna systems for the digital and analog signals, or by multiplexing the digital and analog signals for transmission by a single antenna system. For example, FM radio station 110 broadcasts both analog and IBOC digital content from broadcast location 120. The analog signal can be used by analog receiver 130, and IBOC signal can be used by an IBOC capable receiver 140.
The Federal Communications Commission (FCC) has established various rules regarding the power of the digital broadcast signals in relationship to the power of an analog broadcast, and the National Radio Systems Committee (NRSC) has published power guidelines for FM IBOC, for example NRSC-G202, published September 2010. The FCC rules and the NRSC guidelines describe how much power a digital signal broadcast using IBOC techniques can use, compared to the analog broadcast signal. For example, NRSC-G202 indicates that for symmetric sidebands using service mode MP1, the nominal power of the digital broadcast signal compared to the analog broadcast signal is between −20 dBc (decibels relative to the carrier) and −10 dBc. Translated to percentages, the power of the digital signal is between 1% and 10% of the analog broadcast signal's power. Prior art FIG. 1 illustrates this currently allowed power relationship. It should be noted that other power ratios or relationships can apply for different broadcast modes, and for asymmetrical side-band transmissions.
A benefit of limiting the power of the IBOC digital signals is that interference with analog broadcast signals can be controlled. A drawback is that the lower transmission power of IBOC signals can also limit the area over which the IBOC signals can be reliably received.